Attention has profound effects on visual processing, allowing us to strategically select, filter, and prioritize the vast amount of information in the visual environment. The long-term goal of this project is to understand how the brain shifts attention to visual stimuli. Attention can be shifted in two modes: it can be reflexively "captured" by a salient stimulus, or voluntarily focused by top-down mechanisms on a selected object of interest. This project investigates the roles of the superior colliculus (SC) and frontal eye field (FEF) in reflexive and top-down attention shifts. The SC and FEF are traditionally considered to be areas involved in eye movements. Recent evidence indicates that these brain areas may also be important in controlling shifts of attention in the absence of overt eye movements, but their specific contributions to attention are unclear. Based on anatomy and on their roles in eye movements, we hypothesize that the SC is involved in controlling reflexive attention shifts and the FEF is involved in top-down shifts. We will test this hypothesis, first, by determining whether neural signals recorded in the SC and FEF are appropriate for controlling reflexive or top-down attention shifts. Second, we will ascertain whether these areas play necessary functional roles in attention by examining the impact of temporarily inactivating small regions of either the SC or FEF on reflexive and top-down attention shifts. Finally, attention can produce different types of improvements in visual sensitivity, and we will investigate whether these different effects of attention on perception are separately engaged by the SC and FEF. Relevance: Deficits in attention can seriously impair visual and cognitive functioning, interfere with activities of daily life, and have been associated with greater risk of accident and injury. We expect that the knowledge gained from this project will contribute to a better understanding of the causes of attentional manifestations of human disorders such as unilateral visual neglect, oculomotor apraxia, ADHD, and schizophrenia. Gaining an understanding of the basic neural mechanisms that control attention may provide new avenues for diagnosis, treatment, or rehabilitation of populations suffering from attentional disorders.